Micro-wave detector



P 1966 F. c. DE RONDE 3,274,504

MICROWAVE DETECTOR Filed March 4, 1964 OUTPUT ClRCUIT -f II 15\ 10 .f[III FIGJ ii 3i 1: i w 2 i v i 120 Fl 6. 2 INVENTOR.

FRANS C, DE RONDE AGENT United States Patent 3,274,504 MICRO-WAVEDETECTOR Frans Christiaan de Ronde, Emmasingel, Eindhoven,

Netherlands, assignor to North American Philips Company, Inc., New York,N.Y., a corporation of Delaware Filed Mar. 4, 1964, Ser. No. 349,407Claims priority, application Netherlands, Mar. 21, 1963, 290,518 7Claims. (Cl. 329160) This invention relates to detector devices formicrowaves.

Known detectors in which a conductor connected to a rectifier extends,parallel to the electric lines of force, into or through a wave guide,have the disadvantage that they cause a comparatively high reflection ofthe waves in the waveguide, and their sensitivity differs through abroad range of frequencies.

A microwave detector is known in which a rectifier is connected, inseries with a capacitance forming substantially a short circuit withrespect to microwaves, between opposite points of a circular apertureprovided in a side wall of a wave guide. In this case the rectifier isarranged outside the waveguide proper and also outside the wall thereof.Said device may be made suitable for a broad range of frequencies byplacing the rectifier in a suitably chosen cavity resonator outside thewave guide.

The present invention provides a very efficacious solution of theproblem whereby the reflection coefficient of the detector may be lowerthan that of the known device.

A detector according to the invention employs a rectifier of a kindknown per se. The rectifier is arranged inside a cylindrical shieldingsleeve and has one pole connected to the shielding sleeve and its otherpole connected to a concentric connecting pin. Such so-called coaxialrectifiers are sold commercially.

A detector according to the invention has an aperture provided at acorner in the wall of the wave guide. The rectifier is arranged so thatthe connecting pin extends in a longitudinal bore in the adjacent wallof the wave guide and at right angles to the edge of the corner. Aseries capacitance is formed by a narrow gap between the said shieldingsleeve and further parts of the wall.

In order that the invention may be readily carried into effect, it willnow be described in detail, by way of ex ample, with reference to oneembodiment thereof as shown in the accompanying diagrammatic drawing, inwhich:

FIGURE 1 is a cross-sectional view of a waveguide of rectangular sectionin which a detector is housed; and

FIGURE 2 shows a longitudinal section of the waveguide of FIGURE 1,taken along the plane II-II.

A conductive stub 2 for accommodating a detector 3 is provided at theleft-hand upper corner of a wave guide 1. The stub 2 surrounds anaperture 20 in a waveguide wall 21 at the longitudinally extendingjunction between the wall 21 and the adjoining wall 10. Said stub may beomitted if the wall of the waveguide 1 itself is of sutficientthickness.

The rectifier 3 may be of a kind known per se and FIGURE 1 showsdiagrammatically a cross-section thereof. The detector 3 includes acrystal diode 4, secured to the upper end of a connecting pin 6 which isheld in a circular conductive shielding sleeve 8 by means of aninsulating ring 7. A connecting spring is connected to the sleeve 8 sothat the terminals of the detector are formed by the pin 6 and thesleeve 8.

The pin 6 extends into a vertical bore 9 provided in the middle of theleft-hand side wall 10 of the wave guide 1. The bore 9 extends in atransverse plane of the waveguide which passes through the aperture 20.The shielding sleeve 8 is situated in a circular aperture in the "icestub 2 so that a narrow gap 11 exists between the sleeve 8 and the stub2. This gap has a comparatively high capacity and substantially forms ashort-circuit for microwaves. The gap preferably has a height equal toone quarter of the operational wavelength. The direct out put voltagemay be applied to an output circuit 22 connected between the sleeve 8and the stub 2. Furthermore, as shown in FIGURE 2, an aperture 12 isprovided in the left-hand side wall having a re-entrant portion 13 whichserves as a stop for the ring 7 so that the position of the rectifier isfixed. The reentrant portion 13 of the aperture 12 is aligned with theaperture 20, so that the aperture 12 effectively consists of twoapertures in the wall 10 on opposite sides of the aperture 20 withrespect to the longitudinal direction of the waveguide.

As is well-known, due to the action of waves in a wave guide, currentsflow in the side walls in a direction that is at right angles to theaxis of the wave guide, that is to say vertical in the example shown, asindicated by arrows 14. However, the path of the wall currents isinterrupted at the aperture 12 and these currents thus partly bendaround the aperture and a portion flows through the rectifier 3, asindicated by arrows 15. The rectifier exhibits a certain impedance tothe wall currents so that, if the aperture 12 is small, the path aroundthe aperture is easier for the wall currents than that through therectifier and thus only a very small current will flow through therectifier. If the aperture is made larger, the detour around theaperture becomes larger and a greater proportion of the wall currentswill flow through the rectifier. It has been found that, with suitableproportioning of the aperture, the direct output voltage of the detectormay be made substantially constant through a broad range of frequencies.

In fact, if the aperture has a small length, the sensitivity of thedetector usually decreases with increasing frequency, whereas just thereverse is the case if the aperture is comparatively long, so that thesensitivity is constant for a given intermediate length.

At high frequencies, the impedance of the rectifier is substantiallydetermined by the capacitance between the connecting pin 6 and theshielding sleeve 8. In fact, the impedance of this capacitance iscomparatively low with respect to the impedance of the crystal diode 4itself. The latter impedance exhibits comparatively great differencesfrom rectifier to rectifier because of structural differences. However,since the capacitance between the connecting pin 6 and the shieldingsleeve 8 is comparatively constant the rectifier may be replaced byanother in a simple manner without the frequency response curvesubstantially varying. On the other hand, two different detectors alsoexhibit substantially the same frequency response curve. This propertymay be employed by controlling the strength of a high-frequencyoscillator by means of an output voltage from a first detector deviceand using a second detector device for measuring purposes. The outputvoltage of the second detector device may then be constant throughoutthe X band (8.2 to 12.4 Gc./s.) with a deviation less than 0.3 decibel.The alternating voltage set up across the crystal will usually becomparatively low so that the rectifier operates in the quadraticportion of its characteristic and the direct out- .put voltage isproportional to the square of the field strength in the waveguide, thatis to say proportional to the energy of the waves. The sensitivity is,for example, 10 mv./mw.

The detector according to the invention affords the considerableadvantage that it does not substantially bring about reflection of thewaves in the wave guide, for example at a standing wave ratio (V.S.W.R.)better than 1.01.

This is connected with the fact that, in the arrangement in accordancewith the invention, the supply conductors to the crystal are very shortand hence have little impedance. The impedance of the detector is alsocomparatively low so that only a comparatively low voltage is set upacross the aperture in the side wall and the configuration of the linesof force in the waveguide is also deformed but slightly.

As shown diagrammatically in FIGURE 1, the detector may alternatively bearranged in a partition between the waveguides, the wall parts 16 shownin broken line having to be regarded as belonging to a waveguide placedto the left of the waveguide 1. In this case the direct output voltagewill be proportional to the sum of the wall currents in the two guides.The coupling between the two conductors is comparatively low (forexample from 40 to 60 decibels) despite the aperture in the common sidewall.

The longitudinal bore 9 need not fundamentally be formed in a short sideof the wave guide and may alternatively be provided in a long side, andthe detector device may alternatively be arranged at the corner of aridge in a ridge waveguide.

What is claimed is:

1. Means for detecting high frequency oscillations in a waveguide,comprising a waveguide for conveying high frequency oscillations, saidwaveguide having a rectangular cross-section with first and secondadjacent side walls, said first side wall having a first aperture at thejunction of said first and second side walls, unidirectional currentmeans having first and second terminals, means connecting said firstterminal to said second side wall in the transverse plane of saidwaveguide which extends through said first aperture, capacitor means forcoupling said second terminal to said first side wall in said plane,said second side wall having second and third apertures on oppositesides of said first aperture with respect to the longitudinal directionof said waveguide, whereby wall currents in said waveguide flow throughsaid unidirectional current means, and output circuit means connectedbetween said second terminal and said first side wall.

2. Means for detecting high frequency oscillations in a waveguidecomprising a waveguide for conveying high frequency oscillations, saidwaveguide having first and second longitudinally extending adjoiningwalls, a cylindrical rectifier device of the type having a firstcylindrical end portion comprising a first terminal and joined to asecond cylindrical end portion of larger diameter, the second terminalof said rectifier device being on said second end portion, saidwaveguide having an aperture in said first wall adjacent the junction ofsaid first and second walls, said second wall having a bore at saidjunction in the transverse plane of said waveguide passing through saidaperture, said bore extending within said second wall substantiallynormal to the plane of said first wall, said first end portion beinginserted within said bore, a conductive sleeve surrounding said secondend portion 'and contacting said second terminal, means providing acapacitance between said sleeve and said first wall at said aperture,and output circuit means connected between 'said second terminal andsaid first Wall.

3. Means for detecting high frequency oscillations in a waveguidecomprising a waveguide for conveying high frequency oscillations, saidwaveguide having a rectangular cross-section with first and secondadjoining walls, said first wall having a first aperture adjacent thejunction of said first and second walls, said second wall having secondand third apertures adjacent said junction and overlapping said firstaperture on opposite sides, rectifier means having first and secondterminals, said first terminal being in contact with said second wall atsaid junction and between said second and third apertures, capacitormeans connected between said second terminal and the edges of said firstaperture, and output circuit means connected between said secondterminal and said first wall.

4. The detecting 'means of claim 3, in which said capacitor meanscomprises a conductive sleeve surrounding said rectifier means andspaced from said first aperture, said sleeve being connected to saidsecond terminal.

5. Means for detecting high frequency oscillations in a waveguidecomprising a waveguide for conveying high frequency oscillations, saidwaveguide having a rectangular cross-section with first and secondadjoining walls, said first wall having a first aperture adjacent thejunction of said first and second walls, said second wall havingapertures adjacent said junction and overlapping said first aperture onopposite sides, a stub extending from the edges of said first aperturenormal to said first wall, said second wall having a bore between saidsecond and third apertures and normal to said first wall, a coaxialdiode having a pin comprising one terminal thereof inserted Within saidbore, a conductive sleeve surrounding said diode and being electricallyconnected to the other terminal thereof, said sleeve being within saidstub and forming a capacitor between said stub and other terminal, andan output circuit connected between said other terminal and said stub.

6. A detecting means of claim 5, comprising a second waveguide, whereinsaid second wall is a common wall between said first-mentioned waveguideand said second waveguide, said first aperture extending through a wallof said second waveguide.

7. Means for detecting high frequency oscillations in a waveguidecomprising a waveguide for conveying high frequency oscillations, saidwaveguide having first and second longitudinally extending adjoiningwalls, .a coaxial rectifier device having first and second terminals onopposite ends of a cylindrical body, said first wall having an apertureextending therethrough at the junction of said first and second walls,said second wall having a bore extending from said junction at saidaperture, said bore extending into said second wall substantially normalto said junction, said first terminal of said rectifier device beingwithin said here in contact with said second wall, said second terminalextending externally of said waveguide, capacitive means coupling saidsecond terminal to said first wall externally of said Waveguide, wherebywall currents in said waveguide flow through said rectifier device,output circuit means, and means connecting said output circuit meansbetween said second terminal and said waveguide.

References Cited by the Examiner UNITED STATES PATENTS 2,642,494 6/1953Z-aslaysky et a1. 33383 X 2,956,160 10/1960 Sharpless 329-161 3,028,5604/1962 Saad 329l62 ROY LAKE, Primary Examiner.

A. L. BRODY, Assistant Examiner.

1. MEANS FOR DETECTING HIGH FREQUENCY OSCILLATIONS IN A WAVEGUIDE,COMPRISING A WAVEGUIDE FOR CONVEYING HIGH FREQUENCY OSCILLATIONS, SAIDWAVEGUIDE HAVING A RECTANGULAR CROSS-SECTION WITH FIRST AND SECONDADJACENT SIDE WALLS, SAID FIRST SIDE WALL HAVING A FIRST APERTURE AT THEJUNCTION OF SAID FIRST AND SECOND SIDE WALLS, UNIDIRECTIONAL CURRENTMEANS HAVING A FIRST AND SECOND TERMINALS, MEANS CONNECTING SAID FIRSTTERMINALS TO SAID SECOND SIDE WALL IN THE TRANSVERSE PLANE OF SAIDWAVEGUIDE WHICH EXTENDS THROUGH SAID FIRST APERTURE, CAPACITOR MEANS FORCOUPLING SAID SECOND TERMINAL TO SAID FIRST SIDE WALL IN SAID PLANE,SAID SECOND SIDE WALL HAVING SECOND AND THIRD APERTURES ON OPPOSITESIDES OF SAID FIRST APERTURE WITH RESPECT TO THE LONGITUDINAL DIRECTIONOF SAID WAVEGUIDE, WHEREBY WALL CURRENTS IN SAID WAVEGUIDE FLOW THROUGHSAID UNDIRECTIONAL CURRENT MEANS, AND OUTPUT CIRCUIT MEANS CONNECTEDBETWEEN SAID SECOND TERMINAL AND SAID FIRST SIDE WALL.